1. Field of the Invention
The present disclosure relates to boost circuit technology, and more particularly to a boost circuit having one input voltage and a plurality of output voltages, the LED backlight driving circuit with the boost circuit, and the liquid crystal device (LCD) with the LED backlight driving circuit.
2. Discussion of the Related Art
With the technology revolution, backlight technology of LCDs has been developed. Typical LCDs adopt cold cathode fluorescent lamps (CCFL) as the backlight sources. However, as the CCFL backlight is characterized by attributes including low color reduction ability, low lighting efficiency, high discharging voltage, bad discharging characteristics in low temperature, and also, the CCFL needs a long time to achieve a stable gray scale, LED backlight source is a newly developed technology. For LCDs, the LED backlight source is arranged opposite to the liquid crystal panel so as to provide the light source to the liquid crystal panel. The LED backlight source includes at least one LED string, and each of the LED strings includes a plurality of LEDs serially connected.
FIG. 1 is a circuit diagram of a driving circuit for LED backlight sources of LCDs (“driving circuit”). As shown, the driving circuit includes a boost circuit having an inductor (L), a rectifying diode (D), a Metal-Oxide-Semiconductor (MOS) transistor (Q), and a capacitor (C). One end of the capacitor (C) receives an input voltage (Vin), and the other end of the inductor (L) connects to a positive end of the rectifying diode (D1) and to a drain of the MOS transistor (Q). The gate of the MOS transistor (Q) is driven by a square-wave signals (S), and the drain of the MOS transistor (Q) is electrically grounded. A negative end of the rectifying diode (D) obtains the output voltage (Vo) for providing to the LED string. The negative end of the rectifying diode (D) is electrically grounded via the capacitor (C).
The duty ratio of the square-wave signals (S) of the above driving circuit is d. The relationship between the output voltage (Vo) and the input voltage (Vin) is:
  Vo  =      Vin    ×                  1                  1          -          d                    .      In addition to the high voltage needed for the LED string, the driving circuits usually need more converted voltage. For instance, the voltage needed for the operations of the driving circuit (“VCC”), the reference voltage (Vref), and so on. Currently, a single boost line can only obtain one output voltage.